It is difficult to measure accurately the emissivity or reflectivity of a surface, especially at low grazing angles. The need for reliable measurements is increasing, especially for military vehicles where these physical characteristics (and their control) are significant features for survival. Modern optical (infrared {IR} and visible) seekers detect these “signatures.” Today, measurements of the bidirectional reflectance for an entire vehicle are difficult, expensive, and require a carefully controlled or measured environment.
The present invention addresses a need to measure that IR directional emissivity and reflectivity of surfaces and coatings. The emissivity and bidirectional reflectivity play a major role in determining an airframe's total IR signature. Coatings are often designed to produce particular emissivity/reflectivity characteristics. While techniques exist to measure these properties for small samples in the laboratory, none of these methods are suitable for measuring the properties of the coatings once they are applied to a large airframe.
In U.S. Pat. No. 5,505,543, Rawlings, et al. we described a laboratory emissometer for measuring the emissivity of sample coatings. This device is useful only for small samples and is not suitable for measuring the signature of a vehicle surface. It is, nevertheless, a useful tool for designing coatings. The emissometer operates by measuring the radiation emanating from the surface because of its temperature. This device is capable of measuring normal to grazing angle (0°-80° off normal) emittance spectrally and as a function of temperature between −65° F. and 400° F. 
Surface Optics markets a portable measurement device that operates in the IR. ELDIM's EZContrast® measurement devices uses a CONOSCOPIC approach to obtain high speed measurement of the luminance of liquid crystal displays (LCDs) in the visible at zenith angles of 0-80° and angles of azimuth between 0-360°. ELDIM uses a Fourier lens and a relay lens to focus an image on a cooled CCD sensor to produce a viewing angle map.
Modern aircraft have specifications and requirements for emissivity and reflectivity (based on the IR signature goals) that present new issues relative to the inspection techniques and tools required for manufacturing and maintenance. In particular, the IR signature is affected by the exterior coating reflectance and emittance. The performance of the coating can be sensitive to variations in the coating materials or application processes and to environmental exposure. To assure that an aircraft meets IR specifications, IR coating performance must be tested as applied on the vehicle surface. Such measurements must be repeated on a regular maintenance schedule and after repairs to assure continuing signature performance. These measurements must be nondestructive, rapid, and require minimal skill level and training. Measurement devices should be easily portable (hand-held if possible), affordable, rugged, and require little support (standard power, detect at room temperature).
NDE (nondestructive evaluation) measurements must provide sufficient information to assess whether the surface meets coating and vehicle specifications. It is important that the information be of sufficient content and quality, and only useful information. In addition, the instrument should collect and process the data and provide pass/fail indication to the operator.